memory error

Question

memory error

My iMac had its first kernel panic end of last week. (A grey band gradually descends from the top of the screen, when it has progressed to about 2/3rds of the screen a message pops up prompting to turn the computer off and back on again). This was immediately followed by multiple program crashes, in casu Firefox, at other times Yahoo Messenger, and other programs still (I suppose these programs continuously crashed when they'd been loaded into memory at a faulty address?) . I tried a lot of things, I ran DiskUtility on different occasions, now it reported that the disk was corrupt and prompted me start the system up with the install disk and run DiskUtility and repair the disk from there, but when I did that DiskUtility reported that "the disk appears to be OK". I had mulitiple conflicting verify disk results that way. TechTool on the other hand reported at times a memory error, and then again not. I called AppleCare and they suggested I run Apple Hardware Test, which I did from the Snow Leopard install disk #2. A fraction of a second into testing, AHT (Apple Hardware Test) reported the following:

"Alert: Apple Hardware Test has detected an error

4MEM/4/40000000: 0xb787b018 (this was alternately given as 4MEM/1/40000000: 0xb787b018)"

I took that to mean that one (or several) of the 4 Kingston KTA-MB1333/4G had become defective.

I proceeded to check the memory, and as suggested in an Apple Support article I found online, I started checking the sticks one by one, where I put the first of the sticks in the left bottom compartment (when the iMac faces screen down). To my surprise, at startup, nothing budged: all that was communicated was a series of beeps at regular intervals. I pressed the power button to shut the computer down and tried with a different stick in the same slot (left bottom compartment when the iMac faces screen down). When powered on, the result was the same: a series of beeps. I once again turned the power off and this time tried starting up with the original 2x1 GB Apple memory sticks I had replaced with the Kingston memory upon purchase. The result, again, was the same: nothing more than a series of beeps. When I then replaced the 4 Kingston memory sticks, the computer started up "normally" (except for the occasional kernel panic that is).

Does this mean that it's not the memory that is defect, but the memory slots?

Thank you very much for your insight into this matter.

iMac, Mac OS X (10.7.2), 2.93 GHz Intel Core i7 16 GB RAM

Posted on Dec 20, 2011 1:38 PM

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Answer 1

Kappy

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361,741 points

Dec 20, 2011 1:42 PM in response to Mitchell Tren-ton

It most likely means there is a defective byte in the memory. Whenever that byte is accessed and fails it causes a kernel panic.

Now this could simply mean there is one or more defective modules that need to be replaced.

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Answer 2

Dec 20, 2011 1:48 PM in response to Kappy

Thank you. However, since the machine failed to start up when I used the original Apple 1GB memory sticks in the appropriate slots (memory that hadn't been used since date of purchase), wouldn't that point to the slots being defective rather than the sticks?

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Answer 3

Kappy

Level 10

361,741 points

Dec 20, 2011 1:51 PM in response to Mitchell Tren-ton

It would except that you said when you put back the Kingston modules it would work except for the occasional panic. That's not likely to happen with bad slots.

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Answer 4

Dec 20, 2011 1:54 PM in response to Kappy

Thank you for your diligence. So if the two bottom slots were defective, the machine wouldn't start up at all, even if the top ones were ok and there were memory sticks in all 4 of them?

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Answer 5

Kappy

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361,741 points

Dec 20, 2011 2:01 PM in response to Mitchell Tren-ton

It's possible, but it would depend on what's not working. If slots are defective then you will get beeping at startup:

1 beep = no RAM installed
2 beeps = incompatible RAM types
3 beeps = no good banks
4 beeps = no good boot images in the boot ROM (and/or bad sys config block)
5 beeps = processor is not usable

For the 2007 iMac and later Mac models:

The following table lists the new tones and their meaning:

Tone(s)	Description
1 tone, a 5-second pause, repeat	No RAM installed
3 successive tones, a 5-second pause, 3 successive tones	RAM does not pass data integrity check
1 long tone when holding down the power button	Firmware upgrade in process. See About firmware updates for Intel-based Macsfor more details.
3 long tones, 3 short tones, 3 long tones	Firmware restoration from CD in process. See About the Firmware Restoration CD (Intel-based Macs) for more details.

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Answer 6

Dec 20, 2011 2:17 PM in response to Kappy

I had no idea there were different beep sequences, each with their proper meaning. If I had, I would have paid closer attention. However, from memory, I recall the sequence to have been number one, meaning no RAM installed. But then there would be 2 out of 4 4GB Kingston sticks defective, AND the original 2 1GB Apple sticks (that haven't been used since purchase) as well. Doesn't that seem unlikely? Is it possible that when the slots are defective, the inserted memory is not recognized and the beeps report NO RAM INSTALLED rather than NO GOOD BANKS? Thanks again.

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Answer 7

Kappy

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361,741 points

Dec 20, 2011 2:22 PM in response to Mitchell Tren-ton

If the slots are defective then the memory may not be detected or simply may throw an error. I assume that if the test doesn't find any memory it assumes the slot is good unless it gets a slot error from the onboard firmware.

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Answer 8

Dec 20, 2011 2:25 PM in response to Kappy

Now I'm being told that as a matter of fact the bottoms slots (when screen face down) are not the ones to be used when using only 1 or 2 memory sticks, but that it's the top slots (when screen facing down). If that is so, receiving those no memory installed beeps were very much logical, but it most definitely means that there's faulty information in this article: - http://support.apple.com/kb/ht1423#1 - precisely the one i based my choice of slots upon. Thanks again.

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Answer 9

Kappy

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361,741 points

Dec 20, 2011 2:31 PM in response to Mitchell Tren-ton

Your user manual should show that you install the top slots first, then the bottom ones. I think this note from your article discusses this:

Additional notes i5 and i7 Quad Core iMac computers come with both top memory slots populated. These computers will not start up if only a single DIMM is installed in any bottom slot; these computers should operate normally with a single DIMM installed in any top slot. Core Duo iMac computers should operate normally with a single DIMM installed in any slot, top or bottom. ("Top" and "bottom" slots refer to the orientation of the slots in the pictures below. "Top" refers to the slots closest to the display; "bottom" refers to the slots closest to the stand).

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Answer 10

Dec 20, 2011 2:38 PM in response to Kappy

Well yes, the article says: "top refers to the slots closest to the display", and that's the ones I've used for testing: when I said bottom, I meant the bottom ones when the computer is resting on a surface screen down, in other words: the ones closest to the display. Now I'm being told (by the retailer I bought the Kingston memory from) it would be as a matter of fact the other way round. Thank you.

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Answer 11

Kappy

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361,741 points

Dec 20, 2011 2:44 PM in response to Mitchell Tren-ton

I have two i3 2010 iMacs. The user manuals clearly stated if you only use two modules, then they both had to to in the top slots which are the slots in which your original memory was installed. The top slots are the ones on the top. If you lay the iMac flat with the screen facing the ceiling, then the uppermost slots are the top slots.

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Answer 12

Dec 20, 2011 2:51 PM in response to Kappy

That's the ones I've used when the system returned all those beeps. Why don't they just number and label the darn things. Thanks.

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